INTRODUCTION In Parts 1 and 2 of this series of papers the linear theory of elasticity has been summarized for anisotrop- ic and isotropic materials [1], the fundamentals of micromechanical modeling have been reviewed and rig- orous bounds, dilute approximations and nonlinear rela- tions have been given [2]. In Parts 3 and 4 the effective elastic moduli of polycrystalline alumina and zirconia have been calculated from monocrystal data and com- pared with published values [3] and measured data for porous alumina and zirconia have been analyzed using several fit models, including newly proposed ones [4]. It is the purpose of the present paper to bring all this knowledge together and to predict, analyze and discuss the effective tensile moduli of alumina-zirconia com- posite ceramics (AZ composites), dense as well as porous. In the experimental section the materials and their processing (slip casting and starch consolidation casting for dense and porous AZ composites, respec- tively) are briefly described and the measurement meth- ods applied are mentioned (tensile modulus via the res- onant frequency method, porosity determination via the bulk density measured by the Archimedes method). In the first part of the results section the effective theore- tical density and the effective elastic moduli of dense AZ composites of arbitrary composition are discussed in some detail and handy formulae are given for gene- ral use. In the second part of the results section the effective tensile modulus of two typical AZ composites is investigated in dependence of the porosity: zirconia- toughened alumina with a zirconia content of 15 wt.% (labelled here ZTA) and alumina-containing tetragonal zirconia with a zirconia content of 80 wt.% (labelled here ATZ). The effective tensile modulus is measured by the resonant frequency method and its porosity dependence is analyzed using 11 different fit models. EXPERIMENTAL Dense alumina and alumina-zirconia composite ceramics (AZ composites) were prepared by co-milling mixed aqueous suspensions of submicron alumina and zirconia powders in a high-energy planetary mono mill (Fritsch Pulverisette 6, Germany) and subsequent slip casting of these suspensions (containing 75 wt.% solids) into plaster molds. After demolding and drying the AZ composites were fired at 1530°C. Further processing details can be found elsewhere [5-7]. Original papers Ceramics − Silikáty 49 (2) 77-85 (2005) 77 EFFECTIVE ELASTIC PROPERTIES OF ALUMINA-ZIRCONIA COMPOSITE CERAMICS PART 5. TENSILE MODULUS OF ALUMINA–ZIRCONIA COMPOSITE CERAMICS WILLI PABST, GABRIELA TICHÁ, EVA GREGOROVÁ, EVA TÝNOVÁ Department of Glass and Ceramics, Institute of Chemical Technology in Prague, Technická 5, 166 28 Prague 6, Czech Republic E-mail: [email protected] Submitted November 4, 2004; accepted January 20, 2005 Keywords: Tensile modulus (Young's modulus), Porosity, Dense and porous alumina-zirconia composites, Voigt-Reuss bounds, Hashin-Shtrikman bounds In this fifth and last paper of a series on the effective elastic properties of alumina-zirconia composite ceramics (AZ com- posites) the tensile moduli of dense and porous AZ composites are investigated from the theoretical point of view and com- pared with experimental data. For dense AZ composites the Hashin-Shtrikman bounds turn out to be sufficiently close to each other and excellent agreement is found between theoretically predicted and measured values, so that the arithmetic Hashin- Shtrikman average can be used for predicting effective elastic moduli for arbitrary compositions. For dense zirconia-toughe- ned alumina (ZTA) with 15 wt.% and dense alumina-containing tetragonal zirconia (ATZ) with 80 wt.% of zirconia the theo- retically predicted effective tensile moduli are 375 GPa and 251 GPa, respectively. For porous AZ composites (prepared by starch consolidation casting) the consistency of the experimentally measured data is assessed with regard to the Hashin- Shtrikman upper bound. Fitting results confirm the superiority of the new relation E/E 0 = (1 - φ)·(1 - φ/φ C ), where E is the effective tensile modulus and φ the porosity, over most other fit models. Extrapolated E 0 values are 351 GPa and 237 GPa and critical porosities φ C are 0.796 and 0.882 for porous ZTA and ATZ, respectively.
EFFECTIVE ELASTIC PROPERTIES OF ALUMINA-ZIRCONIA COMPOSITE CERAMICS PART 5. TENSILE MODULUS OF ALUMINA–ZIRCONIA COMPOSITE CERAMICS
Jun 21, 2023
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